The present invention relates to a method and an apparatus for correcting the directional data of streaked patterns such as fingerprints, and more particularly to a method and an apparatus for correcting directional data as instructed by the operator. The invention also relates to a method and an apparatus for correcting the pitch data of streaked patterns such as fingerprints, and more particularly to a method and an apparatus for correcting pitch data as instructed by the operator.
In matching a streaked pattern such as a fingerprint, processing is carried out to clarify the picture of this streaked pattern. For instance in matching a fingerprint, the picture of an obscure latent fingerprint is clarified, and the clarified fingerprint image is matched with the pictures of reference fingerprints stored in a data base. By clarifying the picture of a latent fingerprint, feature points of the fingerprint can be accurately detected, resulting in greater chances for successful fingerprint recognition.
Clarification of a streaked pattern uses data representing the direction (hereinafter referred to as "directional data") of this streaked pattern. Directional data are provided corresponding to each of a plurality of zones into which the streaked pattern are divided. On the basis of these directional data, a mask is prepared to clarify the streaked pattern. Filtering the picture of the streaked pattern with this mask clarifies the picture.
Together with directional data, pitch data are also used for clarifying the picture of a streaked pattern. Pitch data represent the pitch between streaks.
The directional data of a streaked pattern are automatically extracted by moving a search point from a point where the direction is to be detected. Density at the search point varies rapidly when the search point moves across streaks, while density varies slowly when it moves along the streaks. The moving direction of the search point at the time when the density varies least coincides with the direction of streaks.
Pitch data are automatically extracted on the basis of the directional data extracted in the above-described manner. More specifically, pitch data are obtained by calculating the frequency of the density variations of the picture with respect to the direction across the streaks.
As described above, according to the prior art, directional data and pitch data are automatically extracted from the picture of a streaked pattern. However, if the picture is obscure as in the case of a latent fingerprint, the extracted directional data and pitch data are partly inaccurate. Noise in the picture and the relative scarcity of differences in shade make the extraction of these data difficult.
According to the prior art, even if the operator visually detects the inaccuracy of directional data and pitch data, he can not correct it, because manual alteration of data in each zone would require a tremendous amount of labor.